1. Field of the Invention
The present invention relates generally to a data transmitting apparatus and method in a mobile communication system, and in particular, to an apparatus and method for transmitting packet data using Walsh codes in a mobile communication system that supports concurrent transmission of high rate packet data and voice data.
2. Description of the Related Art
Along with the rapid development of mobile technology, mobile communication systems have been developed to additionally provide data service including video conferencing and Internet browsing as well as existing voice service. In a mobile communication system supporting concurrent provision of voice service and data service, the voice service is provided on circuit channels and the data service, on packet channels for efficient data transmission.
Such a system separately uses channel power and orthogonal Walsh codes for the packet data service and the circuit data service (or circuit call service), i.e., the voice service. When the packet data service and the circuit call service are supported at the same time, the latter has priority over the former in using power and orthogonal Walsh codes. Accordingly, power and the numbers of orthogonal Walsh codes assigned to the packet data service and the circuit call service vary with time because of limited power and orthogonal Walsh codes available to a base station. That is, after power and orthogonal Walsh codes are assigned first to the circuit call service, the remaining power and orthogonal Walsh codes are available to the packet data service. As more orthogonal Walsh codes are assigned to the circuit call service, less orthogonal Walsh codes are available to the packet data service. Thus, even if high power can be assigned to the packet data service, shortage of orthogonal Walsh codes may limit the number of modulation symbols transmittable per unit time for the packet data service, thereby decreasing the packet data rate. From the perspective of the capacity of a base station, it is necessary to increase the number of Walsh codes to avoid the case that data cannot be transmitted at a high rate or the case that data transmission is impossible due to shortage of orthogonal Walsh codes, despite enough power.
Therefore, there is a need for a method and apparatus for providing a packet data service using other Walsh codes as well as orthogonal Walsh codes in a forward link transmission system.